I2/CuCl2-promoted one-pot three-component synthesis of aliphatic or aromatic substituted 1,2,3-thiadiazoles

Chemically engineered essential oils prepared through thiocyanation under solvent-free conditions: chemical and bioactivity alteration

The generation of chemically engineered essential oils (CEEOs) prepared from bi-heteroatomic reactions using ammonium thiocyanate as a source of bioactive compounds is described. The impact of the reaction on the chemical composition of the mixtures was qualitatively demonstrated through GC-MS, utilizing univariate and multivariate analysis. The reaction transformed most of the components in the natural mixtures, thereby expanding the chemical diversity of the mixtures. Changes in inhibition properties between natural and CEEOs were demonstrated through acetylcholinesterase TLC autography, resulting in a threefold increase in the number of positive events due to the modification process. The chemically engineered Origanum vulgare L. essential oil was subjected to bioguided fractionation, leading to the discovery of four new active compounds with similar or higher potency than eserine against the enzyme. The results suggest that the directed chemical transformation of essential oils can be a valuable strategy for discovering new acetylcholinesterase (AChE) inhibitors.

I2/DMSO-mediated oxidative C-C and C-heteroatom bond formation: a sustainable approach to chemical synthesis

The I2/DMSO pair has emerged as a versatile, efficient, practical, and eco-friendly catalyst system, playing a significant role as a mild oxidative system, and thus employed as a good alternative to metal catalysts in synthetic chemistry. Presently, I2/DMSO is a thriving catalytic system that is used in preparing C-C and C-X (X = O/S/N/Se/Cl/Br) bonds, resulting in the formation of various bioactive molecules. Many processes utilize this system, including in situ glyoxal synthesis by diverse sp, sp2, and sp3 functionalities via iodination and subsequent Kornblum oxidation. Focusing on oxidation processes, this study examines the synergistic effect of dimethyl sulfoxide (DMSO) and molecular iodine in improving synthetic techniques. We provide a comprehensive overview of the research progress on the I2/DMSO catalytic system for the formation of C-C and C-heteroatom bonds from 2018 to the present. Additionally, the future prospects of this research field are discussed.

Straightforward access to α-thiocyanoketones and thiazoles from sulfoxonium ylides

Efficient, versatile, and metal-free strategies for synthesizing α-thiocyanoketones and thiazoles from β-ketosulfoxonium ylides and ammonium thiocyanate have been described. Due to its simplicity, benign reaction conditions, excellent chemoselectivity, and high yield, this method represents a unique approach for divergent synthesis. Finally, the potential value of the developed methods is demonstrated via large-scale reactions and synthesis of Fanetizole, an anti-inflammatory drug.

I2-Promoted In Situ Cyclization-Rethiolation Reaction: Synthesis of 2-Aliphatic- or Aromatic-Substituted Indolizines

An efficient I₂-promoted one-pot one-step three-component reaction for the synthesis of sulfhydryl indolizines from methyl ketones, 2-pyridylacetate derivatives, and sulfonyl hydrazides via an in situ cyclization-rethiolation strategy has been developed. This protocol shows excellent substrate compatibility, including for chain and cyclic aliphatic methyl ketones, natural product pregnenolone acetate, and phosphorus-containing methyl ketones, affording a series of valuable aliphatic-substituted indolizines in good yields.

Tandem Synthesis of 1,2,3-Thiadiazoles with 3,4-Dichloroisothiazoles and Hydrazines under External Oxidant- and Sulfur-Free Conditions

1,2,3-Thiadiazoles are among the most important heterocyclic motifs, with wide applications in natural products and medicinal chemistry. Herein, we disclose a tandem reaction for the synthesis of structurally diverse 1,2,3-thiadiazoles from 3,4-dichloroisothiazol-5-ketones and hydrazines. This method is characterized by mild external oxidant- and sulter-free reaction conditions, a broad substrate scope, and easy purification.

Magnetic mesocellular foams with nickel complexes: as efficient and reusable nanocatalysts for the synthesis of symmetrical and asymmetrical diaryl chalcogenides

In this work, magnetic mesocellular foam (M-MCF) silica nanoparticles were prepared via inserting magnetic nanoparticles into the pores of mesocellular foams, the inner surface of which was functionalized with a methionine-nickel complex (M-MCF@Met-Ni). The structure of the as-prepared nanocatalysts was studied by FT-IR spectroscopy, BET, TGA, VSM, SEM, HR-TEM, EDS, WDX, XRD, and ICP-OES techniques. Thereafter, this nanocatalyst was used as a new, effective, and magnetically reusable catalyst for C-S and C-Se bond formation under mild conditions. All corresponding products were prepared with good yields and appropriate turnover number (TON) and turnover frequency (TOF), which reveals the high activity of this magnetic nanocatalyst in both reactions. In addition, the recovery and hot filtration tests indicated that this catalyst could be simply separated from the reaction mixture using an outside magnet and reused five consecutive times without any significant loss of its catalyst activity or metal leaching.

Base-promoted anaerobic intramolecular cyclization synthesis of 4,5-disubstituted-1,2,3-thiadiazoles

An alkali-promoted, transition-metal-free and oxidant-free method to construct 4,5-disubstituted-1,2,3-thiadiazoles from N-tosylhydrazone-bearing thiocarbamates by employing a sustainable intramolecular reaction strategy has been developed.

Silver-mediated annulation between 5-H-1,2,3-thiadiazoles and 1,3-dicarbonyl compounds to construct polysubstituted furans

An efficient synthesis of polysubstituted furans by Ag(i)-mediated annulation between 5-H-1,2,3-thiadiazoles and 1,3-dicarbonyl compounds is reported.

Electrochemical Synthesis of 1,2,3-Thiadiazoles from α-Phenylhydrazones

We have developed an electrochemical approach for the synthesis of fully substituted 1,2,3-thiadiazoles from α-phenylhydrazones at room temperature, which is very challenging and complementary to the conventional thermal reactions. The key step involves anodic oxidation of phenylhydrazone derivatives at a constant current followed by N,S-heterocyclization. The protocol is remarkable in that it is free of a base and free of an external oxidant and can be converted to a gram scale for postsynthetic drug development with functional thiadiazoles. Most importantly, the electrochemical transformation reflected efficient electro-oxidation with an operationally friendly easy procedure with ample functional molecules. Cyclic voltammograms support the mechanism of this electro-oxidative cyclization process.

α-Selective C(sp3)-H Thio/Selenocyanation of Ketones with Elemental Chalcogen

A facile method is disclosed for the synthesis of α-thio/selenocyanato ketones through regioselective C-H thio/selenocyanation of ketones. The advantages include the use of easily available starting materials, high efficiency, simple operation, and easy scale-up. Control experiments provide evidence that the reaction proceeded via a radical way, while kinetic isotope effect experiments reveal that the cleavage of the C-H bond serves as the rate-limiting step.

Direct Synthesis of 4-Aryl-1,2,3-triazoles via I2-Promoted Cyclization under Metal- and Azide-Free Conditions

We herein report an iodine-mediated formal [2 + 2 + 1] cyclization of methyl ketones, p-toluenesulfonyl hydrazines, and 1-aminopyridinium iodide for preparation of 4-aryl-NH-1,2,3-triazoles under metal- and azide-free conditions. Notably, this is achieved using p-toluenesulfonyl hydrazines and 1-aminopyridinium iodide as azide surrogates, providing a novel route toNH-1,2,3-triazoles. Furthermore, this approach provides rapid and practical access to potent inhibitors of indoleamine 2,3-dioxygenase (IDO).

Photo-oxidative Ruthenium(II)-Catalyzed Formal [3 + 2] Heterocyclization of Thioamides to Thiadiazoles

An operationally simple and sustainable one-pot photo-oxidative formal [3 + 2] heterocyclization of β-ketothioamides with aryldiazonium salts catalyzed by Ru(bpy)₃Cl₂ has been realized to provide 2,4-disubstituted 5-imino-1,2,3-thiadiazoles in good to high yields under mild reaction conditions for the first time. The reaction proceeded via an α-phenylhydrazone adduct of thioamides leading to 1,2,3-thiadiazoles via N-S bond formation at room temperature. Notably, the products possess Z-stereochemistry with regard to the exocyclic C═N double bond at the 5-position of the ring.

Diiiodine/Potassium Persulfate Mediated Synthesis of 1,2,3-Thiadiazoles from N-Tosylhydrazones and a Thiocyanate Salt as a Sulfur Source under Transition-Metal-Free Conditions

A highly efficient method for the synthesis of 1,2,3-thiadiazoles has been developed by utilizing readily available tosylhydrazones and ammonium thiocyanate with ecofriendly EtOH as the solvent at room temperature. The reaction shows a wide scope of substrates and good functional-group tolerance. This protocol can be scaled up to a gram level and can be applied to coupling reactions with 4-(4-bromophenyl)-1,2,3-thiadiazole as the substrate.

K2S2O8-mediated regio- and stereo-selective thiocyanation of enamides with NH4SCN

A direct and straightforward thiocyanation of enamides with NH₄SCN under metal-free conditions has been accomplished. A variety of (E)-β-thiocyanoenamides are readily produced in a regio- and stereo-selective manner. The protocol features mild reaction conditions, good functional group tolerance and operational simplicity. The potential utility of this strategy was further demonstrated by transformation of thiocyanate into thiotetrazole-containing compounds and a Pd-catalyzed cross-coupling reaction to afford six- or seven-membered sulfur-containing heterocycles. Mechanistic insights into the reaction indicate that the reaction may proceed via a radical mechanism.

Reactions involving aryl methyl ketone and molecular iodine: a powerful tool in the one-pot synthesis of heterocycles

The preparation of heterocyclic compounds has attracted great attention in organic chemistry because of their extensive application in the field of bioactive molecules, materials science, and natural products.

I2/DMSO-Catalyzed Transformation of N-tosylhydrazones to 1,2,3-thiadiazoles

An iodine/DMSO catalyzed selective cyclization of N-tosylhydrazones with sulfur without adding external oxidant was developed for the synthesis of 4-aryl-1,2,3-thiadiazoles. In this reaction, oxidation of HI by using DMSO as dual oxidant and solvent is the key, which allowed the regeneration of I₂, ensuring thus the success of the synthesis. This protocol features by simple operation, high step-economy (one-pot fashion), broad substrate scope as well as scale-up ability.

Iodine-catalyzed efficient synthesis of xanthene/thioxanthene-indole derivatives under mild conditions

An iodine-catalyzed nucleophilic substitution reaction of xanthen-9-ol and thioxanthen-9-ol with indoles has been developed, providing an efficient procedure for the synthesis of xanthene/thioxanthene-indole derivatives with good to excellent yields. This protocol offers several advantages, such as short reaction times, green solvent, operational simplicity, easily available catalyst and mild reaction conditions. Moreover, this method showed good tolerance of functional groups and a wide range of substrates.

An efficient synthesis of xanthene/thioxanthene-indole derivatives has been developed through iodine-catalyzed nucleophilic substitution reaction of xanthen-9-ols and thioxanthen-9-ol with indoles.

I2-Promoted Multicomponent Dicyclization and Ring-Opening Sequences: Direct Synthesis of Benzo[e][1,4]diazepin-3-ones via Dual C-O Bond Cleavage

A novel and efficient formal [4 + 2+1] annulation of aryl methyl ketones and 2-aminobenzyl alcohols for the synthesis of benzo[e][1,4]diazepin-3-ones is reported. This reaction successfully affords diverse seven-membered ring lactams via dual C-O bond cleavage. A preliminary mechanistic study showed that a multicomponent dicyclization and ring-opening sequence might occur, with the introduction of methyl sulfide proposed as the last step. This efficient strategy with mild reaction conditions and a broad substrate scope has potential applications in chemistry and medicine.